This invention relates to photoflash lamps and, more particularly, to flashlamps of the type containing a primer bridge, or the like, ignited by a high voltage pulse.
Such flashlamps typically comprise a tubular glass envelope constricted and tipped off at one end and closed at the other end by a press seal. A pair of lead-in wires pass through the glass press and terminate in an ignition structure including a glass bead, one or more glass sleeves, or a glass reservoir of some type. A mass of primer material contained on the bead, sleeve or reservoir bridges across and contacts the ends of the lead-in wires. Also disposed within the lamp envelope is a quantity of filamentary metallic combustible, such as shredded zirconium or hafnium foil, and a combustion supporting gas, such as oxygen, at an initial fill pressure of several atmospheres.
Lamp functioning is initiated by application of a high voltage pulse (e.g., several hundred to several thousand volts as, for example, from a piezoelectric crystal) across the lamp lead-in wires. The mass of primer within the lamp then breaks down electrically and ignites; its deflagration, in turn, ignites the shredded combustible which burns actinically.
Several different constructions for high voltage flashlamps have been described in the prior art. The following U.S. Pat. Nos. are examples: 2,718,771; 2,768,517; 2,771,765; 2,868,003; 3,000,200; 3,312,085; 3,501,254; 3,556,699; 3,602,619; 3,627,459; 3,685,947; 3,721,515; 3,823,994; 3,873,260; 3,873,261; and 3,884,615. All of these constructions have either been difficult to fabricate, contained extra and costly glass components, or suffered from shred-caused preflash short circuits. Some of the referenced constructions are not adaptable to miniaturization and use in multilamp flash devices of modern design. Many require the use of intricate, tiny glass parts that are very expensive, difficult to feed, and to orient and slip over the lead wires on automated high speed lamp making machinery. Reliable automated primer application would not be feasible with some of the designs. Other designs would so vary in firing voltage from one lamp to another that reliable operation could not be attained with the voltages and energy levels available from miniaturized piezoelectric sources that would fit in the present small cameras. Some of the constructions fail to recognize the problem of shred shorting or shred interference with ignition.